In recent years, mobile devices such as cell-phones (and in particular smart-phones), tablets and laptops have become ubiquitous. Most of these devices include one or two compact cameras: a main rear-facing camera (i.e. a camera on the back side of the device, facing away from the user and often used for casual photography) and a secondary front-facing camera (i.e. a camera located on the front side of the device and often used for video conferencing).
Although relatively compact in nature, the design of most of these cameras is very similar to the traditional structure of a digital still camera, i.e. they comprise an optical component (or a train of several optical elements and a main aperture) placed on top of an image sensor. The optical component (also referred to as “optics”) refracts the incoming light rays and bends them to create an image of a scene on the sensor. The dimensions of these cameras are largely determined by the size of the sensor and by the height of the optics. These are usually tied together through the focal length (“f”) of the lens and its field of view (FOV)—a lens that has to image a certain FOV on a sensor of a certain size has a specific focal length. Keeping the FOV constant, the larger the sensor dimensions (e.g. in a X-Y plane) the larger the focal length and the optics height.
In addition to the optics and sensor, modern cameras usually further include mechanical motion (actuation) mechanism for two main purposes: focusing of the image on the sensor and optical image stabilization (OIS). For focusing, in more advanced cameras, the position of the lens module (or at least one lens element in the lens module) can be changed by means of an actuator and the focus distance can be changed in accordance with the captured object or scene. In these cameras it is possible to capture objects from a very short distance (e.g., 10 cm) to infinity. The trend in digital still cameras is to increase the zooming capabilities (e.g. to 5×, 10× or more) and, in cell-phone (and particularly smart-phone) cameras, to decrease the pixel size and increase the pixel count. These trends result in greater sensitivity to hand-shake or in a need for longer exposure time. An OIS mechanism is required to answer the needs in these trends.
In OIS-enabled cameras, the lens or camera module can change its lateral position or tilt angle in a fast manner to cancel the handshake during the image capture. Handshakes move the camera module in 6 degrees of freedom, namely linear movements in three degrees of freedom (X, Y and Z), pitch (tilt around the X axis), yaw (tilt around the Y axis) and roll (tilt around the Z axis). FIG. 1 shows an exemplary classical four rod-springs (102a-d) OIS structure in a single-aperture camera module 100. The four rod-springs are rigidly connected to an upper frame 104 which accommodates usually an AF actuator (not shown) that moves the lens module 106. This structure allows desired modes of movement in the X-Y plane (translation), FIG. 1a, but also allows a mode of unwanted rotation (torsion) around the Z axis, FIG. 1b. The latter may be due to a combination of several causes such as asymmetric forces applied by the coils or by a user's (or phone) movements, imperfections of the rod-springs and the high rotational compliance of the four-spring rod-spring+frame structure.
In the case of a centered single-aperture camera module, the rotation around the Z axis (according to the exemplary coordinate system shown in FIG. 1) does not affect the image quality severely, since the lens is axisymmetric. However, this does affect OIS in a dual-camera module, FIG. 2A. FIG. 2A shows in (a) a rotation mode around an axis 202 (in the figure, parallel to the Z axis) that is roughly centered between two camera modules 204 and 206 of a dual-aperture camera 200. Because of the location of rotation axis 202, the rotation may cause significant deterioration of the image quality. The rotation causes each lens to shift away in undesired directions (shown by arrows in FIG. 2A(b)) in an unpredictable way. The result is motion blur of the image and a shift of the two lenses in opposite Y directions that results in decenter between images received by each camera module and therefore potentially in a catastrophic influence on fusion algorithm results.
Yet another problem may occur in a folded optics zoom dual-aperture camera, such as a camera 250 shown in FIG. 2B. Such a camera is described for example in detail in co-owned international patent application PCT/IB2016/052179. Camera 250 includes a “folded” camera module 252 with a first optical axis 270 and an upright (non-folded) camera module 254 with a second optical axis 272 perpendicular to axis 270. A 90° folding of an optical path parallel to axis 272 to an optical path parallel axis 270 is performed by an optical path folding element (OPFE) 274. The OPFE may exemplarily be a prism or mirror. Among other components, folded camera module 252 comprises a lens actuation sub-assembly for moving a lens module 256 (and a lens therein, which is referred to henceforth as “folded lens”) in the X-Y plane. The lens actuation sub-assembly includes a hanging structure with four flexible hanging members (i.e. the “rod-springs” referred to above) 258a-d that hang lens module 256 over a base 260. In some exemplary embodiments, hanging members 256a-d may be in the form of four wires and may be referred to as “wire springs” or “poles”. The hanging structure allows in-plane motion as known in the art and described exemplarily in co-owned U.S. patent application Ser. No. 14/373,490. Exemplarily, a first movement direction 262 of the lens is used to achieve AF and a second movement direction 264 is used to achieve OIS. A third movement, an unwanted rotation 266 of the lens about an axis parallel to the Z axis as described above actually causes an unwanted effect of dynamic tilt of the lens (the lens' optical axis may not be perpendicular to the sensor's surface due to that rotation) and may result in images that are usually sharp on one side and blurry on the other side. The actuators in such cameras are typically voice coil magnet (VCM) actuators. A major problem with known VCMs that provide (X, Y)-direction OIS movement and Z-direction AF movement is that the VCMs are larger along the X and Y axes than the moved lens module.
It would be advantageous to have a folded camera module with both AF and OIS mechanisms, where the incorporation of such mechanisms and capabilities should follow standard manufacturing processes and should not result in penalty in camera height. It would be further advantageous to have a folded-lens dual-aperture camera that incorporates such a folded camera module.